how to test a used bass ampli to buy it?

first test it at low volumes. Listen to the tone. Do you like it?

Try louder volumes. How much does the tone change? Listen for distortion, speaker buzzing, any weird noise is just that, weird. You should always test an amp at the volume you intend to use it. If they won't let you crank it, try somewhere else.

Manipulate every pot and slider to make sure each works properly and there are no pops or cracks.

Visually inspect the speaker. Especially around the outer edges. They can only soak up so many beers before they start sounding funny.

Lastly and most importantly: SMELL IT!!!!

Always good advice for any electronic. Heat is the number one killer or electronics. (and you thought it was drunk driving) If you smell a slight burning smell or the smell of heated plastic, etc, You may want to pass on the amp.

I always visually inspect the piece as a whole. I operate under the assumption that if a person abuses the outside of the amp, they are likely to abuse the inside. I may have missed out on some deals by operating like this, but I have also never bought a lemon amp. Sure, an amp that has been gigging with a great deal is going to get beat up, but even that tells you that the amp has seen a great deal of use.

Chas

 

You should also check the internet for reviews on the product before you by or even test it. There are countless numbers of them out there.

Chas

 

Aside from giving it a thorough once-over, I highly recommend that you bring YOUR bass in to try it. Grabbing whatever's handy won't give you a true representation of what you're going to be using it for.

 

Absolutely second that.